This application claims priority to Japanese Application No. 2000-353961, filed Nov. 21, 2000, the entire disclosure of which is hereby incorporated by reference herein.
1. Field of the Invention
The present invention relates to a personal watercraft. More particularly, the present invention relates to an improved exhaust system for a personal watercraft.
2. Description of the Related Art
Personal watercraft have become very popular in recent years. This type of watercraft is sporting in nature and typically is configured to carry a rider and possibly one to three passengers. A relatively small hull of the personal watercraft commonly defines a riders"" area and an engine compartment, which lies below the riders"" area. An internal combustion engine frequently powers a jet propulsion unit, which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on the underside of the watercraft hull. The jet propulsion unit is located within the tunnel and is driven by a drive shaft. The drive shaft usually extends between the engine and the jet propulsion device, through a wall of the hull tunnel.
Recently, the use of personal watercraft has been restricted on some bodies of water. Some proponents of the restrictions cite operation noise. Primarily because of the small size of personal watercraft, a relatively simple exhaust system generally is used, which does not provide a significant degree of silencing. In addition, because the small personal watercraft can be used on quite small bodies of water, the perceived noise levels may be greater than larger watercraft having unmuffled exhaust systems but which do not operate on these small bodies of water.
An exhaust system of a typical personal watercraft discharges engine exhaust to the atmosphere either through or close to the body of water in which the watercraft is operating. In one arrangement, the exhaust is discharged through a discharge opening formed in a rearwardly opening pump chamber, which surrounds the jet propulsion unit and a rear portion of the tunnel. The exhaust passes from the opening to the body of water along side the jet propulsion unit. Although this discharge arrangement successfully reduces exhaust noise under some conditions, there are problems associated with this arrangement. For example, as the watercraft turns, water from the jet propulsion unit can be directed into the space between the pump chamber and the tunnel. This water can lead to choking in the exhaust system, which can adversely affect engine performance. In addition, when the watercraft is accelerated to planing speeds, the discharge opening can be exposed to atmosphere. This typically results in an increase in noise pollution.
A need therefore exists for an improved exhaust system for a personal watercraft, which reduces noise pollution from the watercraft without adversely effecting engine performance.
Therefore, one aspect of the present invention involves a small watercraft that comprises a hull having a longitudinal axis and an engine disposed within the hull. A tunnel is defined on an underside of the hull. A propulsion is driven by the engine and includes a jet pump unit disposed at least partially within the tunnel. An exhaust system communicates with the engine and extends to and terminates at an exhaust discharge outlet to discharge exhaust gases generated by the engine. The exhaust discharge outlet is located along the tunnel such that the exhaust gases are discharged into a space defined between the tunnel and the jet pump unit. An exhaust opening is located downstream of the exhaust discharge outlet and is defined between the tunnel and the jet pump unit. A barrier is located in the exhaust opening so as to form an exhaust sub-chamber in the tunnel upstream of the barrier.
Another aspect of the present invention involves a small watercraft that comprises a hull having a longitudinal axis and an internal combustion engine disposed within the hull. A tunnel is defined on an underside of the hull. A propulsion device is driven by the engine and includes a jet pump unit disposed at least partially within the tunnel. An exhaust system communicates with the engine and extends to and terminates at an exhaust discharge outlet to discharge exhaust gases generated by the engine. The exhaust discharge outlet is located on the tunnel such that the exhaust gases are discharged into a space defined between the tunnel and the jet pump unit. The watercraft further including means for forming an exhaust sub-chamber within the space to reduce exhaust gas noise.
Yet another aspect of the present invention involves a small watercraft that comprises a hull. A recess is formed in a lower surface of the hull. A propulsion unit is mounted within the recess. An engine drives the propulsion unit. An exhaust system extends between the engine and the recess. The recess extends rearward to an outlet. A barrier is disposed around a portion of the propulsion unit at a location in the recess that is upstream of the outlet.
It should also be noted that all of these aspects are intended to be within the scope of the invention herein disclosed. These and other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description of two preferred embodiments with reference to the attached figures, the invention not being limited to the particular preferred embodiments disclosed.